Unpublished Mediterranean and Black Sea records of marine alien, cryptogenic, and neonative species

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020–2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia).peer-reviewe

Experimental Investigation of Stainless Steel SAE304 Laser Engraving Cutting Conditions

Laser machining processes are a new entrant and a rapidly evolving type of non-conventional machining process which allows the machining of complex geometries with high precision, surface quality and productivity in a wide range of materials. Thus, the need for creating a method has emerged that will help the laser machine operator to select the optimal process parameters. In this study an experimental investigation of the effect of the process parameters on the effectiveness of the laser engraving process was held. The examined process parameters were namely the average output power, the repetition rate, and the scanning speed. For this purpose 126 experimental samples, with various combinations of process parameters using a nanosecond Nd:YAG DMG MORI Lasertec 40 laser machine on a SAE 304 stainless steel plate were made. The measured criteria which evaluated the effectiveness of the process were the removed material layer thickness and the material removal rate

Modeling and simulation of the nanosecond pulsed laser engraving process

Ιn this paper a 3D finite element simulation model of the nanosecond pulsed laser engraving process will be presented. With this model simulations of laser engraving process will be performed for some widely used materials using a wide range of process parameters in order to estimate the removed material layer thickness at each laser scan over the surface of the workpiece. Determining the removed material layer thickness is an important task because the machine must receive this value as input from the operator to calculate how many passes-layers need to be made in order to achieve the desired final depth of engraving. Since there is no simulation tool for this purpose at this time, the removed material layer thickness is determined through an experimental procedure. However, this procedure is time consuming as it has to be carried out each time separately depending on the process parameters, the material used, etc

Finite element method simulation of laser engraving

In the present thesis an experimentally confirmed finite element method (FEM) simulation model for nanosecond pulsed laser engraving process is developed. The main purpose of the simulation model is the prediction of the final engraving geometry and the optimization of the process by studying the effect of the process parameters on machining quality and productivity. A general heat transfer model was adopted where the incident laser beam causing the material ablation was modeled using a gaussian heat source. The effect of the laser beam inclination and convergence were taken into account. The laser map containing the positions of the laser beam pulses to be sent was generated according to the unidirectional cross hatching strategy. Τhe Q-switching mechanism was modeled to define the intensity of the laser beam over the time. The laser beam absorption was modeled considering the loses due to the material reflectivity and the plasma shielding by the interaction of the incident laser beam and the generated metal vapour plasma plume. The ablation mechanism was modeled using a moving mesh method to define the geometry shape changes caused by the evaporative removal of material. Laser engraving simulation tests were performed for materials such as stainless steel SAE304, pressure vessel steel P355GH, yellow brass C26000, aluminium Al7075-T6 for various combinations of basic process parameters: average power, scanning speed, repetition rate. From the simulations the engraving geometry was predicted in the same way as it would be formed if the process was performed in practice in real conditions in a laser machining center. In addition, removed material layer thickness and material removal rate values were predicted for each case. Furthermore, the imperfections-defects that appear in the engraved geometry due to kerf formation were predicted such as the slope that appears on the side walls by calculating the values of kerf taper angle, top kerf width and bottom kerf width. The simulations results were examined and conclusions were drawn about the effect of the process parameters on the laser engraving process outcome.To validate the simulation model laser engraving experiments were performed for the purpose of comparing the experimental with the simulation results. The experiments were conducted using the DMG MORI LASERTEC 40 nanosecond pulsed Q-switched 1064nm laser engraving machine and measured using the Bruker Contour GT-K 3D optical profilometer. The experimental results positively validated the simulation model.Στην παρούσα διδακτορική διατριβή παρουσιάζεται η ανάπτυξη ενός πειραματικά επιβεβαιωμένου μοντέλου προσομοίωσης της κατεργασίας χάραξης με παλμούς δέσμης Laser διάρκειας νανοδευτερολέπτων κάνοντας χρήση της μεθόδου των πεπερασμένων στοιχείων. Στόχος είναι η πρόβλεψη της τελικής γεωμετρίας χάραξης και η βελτιστοποίηση της κατεργασίας μελετώντας την επίδραση των συνθηκών κατεργασίας στην ποιότητα του κατεργασμένου τεμαχίου και την παραγωγικότητα της διαδικασίας. Χρησιμοποιήθηκε ένα γενικευμένο μοντέλο μετάδοσης θερμότητας στο οποίο η προσπίπτουσα δέσμη Laser που είναι υπεύθυνη για την αφαίρεση του υλικού, μοντελοποιήθηκε ως μια πηγή με κατανομή Gauss λαμβάνοντας υπόψη τις μεταβολές από την κλίση αλλά και τη σύγκλησή της. Ο χάρτης σάρωσης που εμπεριέχει τις θέσεις στις οποίες πρόκειται να σταλούν οι παλμοί της δέσμης δημιουργήθηκε σύμφωνα με την μονοκατευθυντική διασταυρούμενη στρατηγική σάρωσης. Μοντελοποιήθηκε η παλμική συμπεριφορά της δέσμης λόγω της τεχνικής μεταγόμενου Q για τον ορισμό της πυκνότητας ισχύος συναρτήσει του χρόνου. Μοντελοποιήθηκε ο μηχανισμός απορρόφησης της δέσμης λαμβάνοντας υπόψη τις απώλειες λόγω της ανακλαστικότητας του υλικού, τις απώλειες λόγω της θωράκισης της δέσμης κατά τη διέλευσή της από το πλούμιο πλάσματος ατμών μετάλλου και τη ροή θερμότητας που επιστρέφει στο τεμάχιο λόγω της ακτινοβολίας που εκπέμπεται από το πλάσμα. Ο μηχανισμός αφαίρεσης υλικού μοντελοποιήθηκε χρησιμοποιώντας μια τεχνική μετακίνησης πλέγματος για τον προσδιορισμό των αλλαγών της γεωμετρίας που προκαλούνται από την ατμοποίηση του υλικού. Προσομοιώσεις χαράξεων πραγματοποιήθηκαν για υλικά όπως ανοξείδωτος χάλυβας SAE304, χάλυβας κατασκευής δοχείων πίεσης P355GH, ορείχαλκος C26000 και κράμα αλουμινίου Al7075-T6 για διάφορους συνδυασμούς των βασικών συνθηκών κατεργασίας: μέση ισχύς, ταχύτητα δέσμης και συχνότητα επανάληψης παλμών. Από τις προσομοιώσεις προβλέφθηκε η γεωμετρία χάραξης με τον ίδιο τρόπο όπως αυτή θα σχηματιζόταν εάν η κατεργασία πραγματοποιείτο στην πράξη, σε πραγματικές συνθήκες σε ένα κέντρο κατεργασιών Laser χάραξης. Επιπλέον, για κάθε περίπτωση, υπολογίστηκαν οι τιμές του πάχους στρώματος αφαίρεσης υλικού και του ρυθμού αποβολής υλικού. Επιπλέον έγινε μια εκτίμηση των ατελειών που εμφανίζονται στη γεωμετρία χάραξης λόγω λοξοποίησης (kerf), όπως η κλίση που εμφανίζεται στα πλευρικά τοιχώματα υπολογίζοντας τις τιμές της γωνίας κλίσης των τοιχωμάτων αυτών καθώς και του άνω πλάτους χάραξης και του κάτω πλάτους χάραξης. Τα αποτελέσματα των προσομοιώσεων μελετήθηκαν διεξοδικά και εξήχθησαν συμπεράσματα σχετικά με την επίδραση των συνθηκών κατεργασίας στο τελικό αποτέλεσμα της κατεργασίας χάραξης. Για την επιβεβαίωση του προσομοιωτικού μοντέλου ένας μεγάλος αριθμός από πειραματικές χαράξεις πραγματοποιήθηκαν με σκοπό τη σύγκριση μεταξύ των πειραματικών αποτελεσμάτων και αυτών από τις προσομοιώσεις. Οι χαράξεις υλοποιήθηκαν με τη χρήση του κέντρου κατεργασιών Laser χάραξης DMG MORI LASERTEC 40 και μετρήθηκαν με τη χρήση του τρισδιάστατου οπτικού προφιλόμετρου Bruker Contour GT-K. Τα πειραματικά αποτελέσματα επιβεβαίωσαν την ορθή λειτουργία και την υψηλή ακρίβεια του προσομοιωτικού μοντέλου

Experimental Investigation of Stainless Steel SAE304 Laser Engraving Cutting Conditions

Laser machining processes are a new entrant and a rapidly evolving type of non-conventional machining process which allows the machining of complex geometries with high precision, surface quality and productivity in a wide range of materials. Thus, the need for creating a method has emerged that will help the laser machine operator to select the optimal process parameters. In this study an experimental investigation of the effect of the process parameters on the effectiveness of the laser engraving process was held. The examined process parameters were namely the average output power, the repetition rate, and the scanning speed. For this purpose 126 experimental samples, with various combinations of process parameters using a nanosecond Nd:YAG DMG MORI Lasertec 40 laser machine on a SAE 304 stainless steel plate were made. The measured criteria which evaluated the effectiveness of the process were the removed material layer thickness and the material removal rate

FEM modeling simulation of laser engraving

Summarization: In this paper, a 3D simulation model for nanosecond pulsed laser engraving process is developed, using the finite element method (FEM) aiming at the prediction of the final geometry of the workpiece and optimizing the process. A general heat transfer model is adapted where the incidence laser beam causing the material ablation is modeled using a Gaussian surface heat source, taking into account the interaction between the laser beam, the workpiece material, and the generated metal-vapor plasma. To validate the simulation model, a large set of experiments was performed for the purpose of comparing the experimental with the simulation results. The experiments were conducted on stainless steel and a pressure vessel steel plate using the DMG MORI Lasertec 40 machine for various combinations of the three machining process parameters: average power, repetition rate, and scanning speed. The experimental results positively validated the simulation model. Τhe numerical results were examined and some conclusions were drawn about the effect of the machining parameters on the laser engraving process.Παρουσιάστηκε στο: International Journal of Advanced Manufacturing Technolog

FEM modeling and simulation of kerf formation in the nanosecond pulsed laser engraving process

Summarization: In the present study, a finite element method (FEM) simulation model is developed for nanosecond pulsed laser engraving process. The model’s novelty lies in the fact that it predicts the actual dimensions of the engraved geometry emphasizing the dimensional deviation due to the defects from kerf formation such as the sloped side walls instead of the intended vertical ones. Simulations were performed and the values of kerf taper angle, top kerf width and bottom kerf width were compared with the corresponding ones from experimental tests made using a LASERTEC 40 laser engraving machine and also were used for process optimization.Presented on: CIRP Journal of Manufacturing Science and Technolog